When it comes to saying “No!” to guests who mess with your wedding plans, you should always be as polite and considerate as possible, says Peggy Post, author of “Emily Post’s Wedding Etiquette” (William Morrow, 6th edition; 2014), even if you’re dealing with someone who’s being difficult or presumptuous.

If, for example, you don’t include the names of children on the invitation (the proper indication that they’re not invited) but a parent writes their names on the RSVP card, Post suggests clearing up the matter with a face-to-face conversation or a phone call. Explain that you’re very sorry, but you aren’t inviting children to your wedding and making an exception would upset other guests. If there’s a reason, such as the venue doesn’t allow kids or you’re on a tight budget, you may share it, but express it in a way that’s informative rather than defensive. Close by telling the guest you really hope they can still join you.

If they threaten that they’ll have to miss the event, simply apologize again and say “We will miss you!” says Elena Brouwer, director of the International Etiquette Centre, Hollywood, Florida.

The same advice applies to saying no to single guests who incorrectly assume they can bring any date they like. “But,” Brouwer adds, “if they do opt to come, be sure to seat them with their close friends or other single people.”

As for guests who try to get involved in your planning or offer services you don’t want, Post recommends listening to them with an open mind. If you’re not interested, graciously explain that while you truly appreciate their opinion or offer, you already know what you’re doing – and stand your ground, says Post. “At the end of the day, a wedding should always be about the couple.”